1. Field of the Invention
The present invention relates in general to a resistance ceramic heater, an electrochemical element incorporating such a ceramic heater, and an oxygen alanyzing device using such an electrochemical element, and more particularly to a resistance ceramic heater which has improved durability or prolonged life expectancy.
2. Discussion of the Prior Art
A resistance ceramic heater is known according to Laid-Open Publications Nos. 61-109289 (published in 1986), 61-138487 (published in 1986) and 60-212986 (published in 1985) of unexamined Japanese Patent Applications. In the ceramic heater disclosed in these publications, a resistance heating element consisting of an electrically resistive heat-generating conductor, and electrical leads for supply power to the heating element are formed in desired patterns, integrally on a surface of a ceramic substrate. The heating element is generally formed on the ceramic substrate, for example, by screen printing of an electrically conductive material (metal) such as tungsten or platinum. The electrically resistive heat-generating conductor is energized with an electric current supplied thereto from an external power source through the electrical leads, to produce heat based on the electrical resistance of the heat-generating conductor, for heating a desired article or member.
The resistance heating element formed in a suitable pattern may have some defects or flaws at its local portions, for some reason or other in the process of manufacture as by screen printing technique. For example, some portions of the heating element may have an extremely small thickness due to inadequate printing condition, or an abnormally high electrical resistance value due to inclusion of a foreign substance in the material. When the heating element (heat-generating conductor) is energized, a voltage across a defective portion of the element is abnormally or extremely raised, whereby the electrically conductive metal at the defective portion is overheated, sintered or cracked, and may consequently be electrically disconnected. Thus, the defects of the heating element lead to a considerably shortened life expectancy or extremely lowered durability of the ceramic heater.